System and method for determining a fill status of a canister of fluid in a reduced pressure treatment system

ABSTRACT

A reduced pressure treatment system is provided that includes a canister that is fluidly connected to a tissue site and is configured to receive fluid drawn from the tissue site under the influence of a reduced pressure. A reduced pressure source provides the reduced pressure and is fluidly connected to the tissue site by a fluid communication path, which may include a source conduit, the canister, and a target conduit. A sensing device communicates with the source conduit and is configured to sense a pressure in the source conduit. A valve communicates with the source conduit and is configured to vent the reduced pressure. A processing unit communicates with the sensing device and the valve and is configured to open the valve for a selected amount of time, determine a decay of reduced pressure, and determine a fill status of the canister based on the decay of reduced pressure.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/265,571, filed Apr. 30, 2014 now U.S. Pat. No. 9,199,011, which is acontinuation of U.S. application Ser. No. 13/733,778, filed Jan. 3, 2013now U.S. Pat. No. 8,747,376 which is a divisional of U.S. applicationSer. No. 11/901,664, filed Sep. 18, 2007 now U.S. Pat. No. 8,366,690,which claims the benefit of U.S. Provisional Application No. 60/845,993,filed Sep. 19, 2006, which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to medical devices and morespecifically to detection methods and systems for determining a fillstatus of a canister of fluid used with medical devices.

2. Description of Related Art

The treatment of open wounds and sores such as decubitis ulcers andthose ulcers found on the feet of diabetics is problematic. Propertreatment of such wounds which are frequently infected with bacterialpathogens is multifactorial. Surgery is usually required to remove deadand necrotic tissue. Antibiotics are used to inhibit the growth or killthe pathogenic bacteria, if possible. At the same time, proper nutritionis necessary to maintain the health status of the patient and moreimportantly, proper wound care is essential to healing of the wound orsore.

Proper wound care requires keeping the wound clean and dry. When thewound is infected, the underlying tissue expresses serous fluids andpossibly a purulent exudate, both of which have to be removed to promotewound healing. Traditional methods of removing the aforementioned fluidsrequired a mechanical scrubbing of the wound and drying of the woundwith sponges. This procedure is not only painful for the patient butalso increases the possibility of superinfection of the wound bybacteria introduced into the wound during treatment.

An alternative to this mechanical scrubbing of the open wound is anegative pressure wound closure device. This negative pressure woundclosure device consists of a foam pad which is placed over the wound toform a relatively air tight and leak proof seal around the wound. Thenegative pressure wound closure device also has a vacuum pump fluidlycoupled to the pad which is seated over the patient's wound. When thevacuum pump is activated, a negative pressure is created inside the padcovering the wound. The fluids expressed by the wound are removedthrough the foam pad by the negative pressure and transported through atube connecting the foam pad to a canister. The canister collects thefluids removed from the wound. When the canister is full of fluidremoved from the wound, the canister is emptied and reengaged to thevacuum system. Attempts have been made to alert the user when thecanister is full of wound fluid. These methods have been aimed atdirectly measuring the amount of wound fluid in the canister.

However, existing methods of directly measuring the amount of woundfluid in the canister have proved unreliable because, generally, thewound fluid is viscous. The fluid also frequently foams, bubbles, andtraps air, which may result in the fluid not settling to the bottom ofthe canister. There remains a need in the art for a reliable system andmethod to alert the user when the canister for collection of wound fluidis full and in need of emptying.

SUMMARY OF THE INVENTION

The problems with existing canister detection systems are solved by thesystems and method of the present invention. In accordance with oneembodiment of the present invention, a method for detecting a fillstatus of a canister of fluid in a tissue treatment system is provided.The method includes creating a reduced pressure in a fluid communicationpath of the tissue treatment system and applying the reduced pressure toa tissue site. Fluid is collected from the tissue site in the canister.The reduced pressure is released, and a decay of the reduced pressure ismeasured. A fill status of the canister is determined from the measureddecay.

In another embodiment of the present invention, a reduced pressuretreatment system includes a canister fluidly connected to a tissue siteand configured to receive fluid drawn from the tissue site under theinfluence of a reduced pressure. A reduced pressure source is configuredto provide the reduced pressure and is fluidly connected to the tissuesite by a fluid communication path. The fluid communication pathincludes a source conduit, the canister, and a target conduit. Thecanister is positioned between the reduced pressure source and thetissue site and is fluidly connected to the reduced pressure source bythe source conduit. The canister is also fluidly connected to the tissuesite by the target conduit. The reduced pressure treatment systemfurther includes a sensing device in communication with the sourceconduit and configured to sense a pressure in the source conduit. Avalve is provided in communication with the source conduit toselectively vent the reduced pressure. A processing unit is incommunication with the sensing device and the valve. The processing unitis configured to open the valve for a selected amount of time, receivesensing data from the sensing device during the selected amount of timeto determine a decay of reduced pressure, and determine a fill status ofthe canister based on the decay of reduced pressure.

In still another embodiment of the present invention, a reduced pressuretreatment system includes a reduced pressure source to provide a reducedpressure. A porous pad is positioned at the tissue site and is fluidlyconnected to the reduced pressure source. A canister is fluidlyconnected between the porous pad and the reduced pressure source tocollect fluid drawn from the tissue site. The system further includes asolenoid valve that is fluidly connected to a conduit between thecanister and the reduced pressure source. Means is provided fordetermining a pressure decay in the conduit when the solenoid valve isopened.

Other objects, features, and advantages of the present invention willbecome apparent with reference to the drawings and detailed descriptionthat follow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a reduced pressure treatment system having full canisterdetection capabilities according to an embodiment of the presentinvention;

FIG. 2 depicts a block diagram of a processing unit of the reducedpressure treatment system of FIG. 1;

FIG. 3 depicts a graphical representation of the results of a testconducted with a system employing a full canister detection methodaccording to an illustrative embodiment of the present invention;

FIG. 4 depicts a graphical representation of the results of a testconducted with a system employing a full canister detection methodaccording to an illustrative embodiment of the present invention;

FIG. 5 depicts a graphical representation of the results of a testconducted with a system employing a full canister detection methodaccording to an illustrative embodiment of the present invention; and

FIG. 6 depicts a graphical representation of the results of a testconducted with a system employing a full canister detection methodaccording to an illustrative embodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In the following detailed description of the illustrative embodiments,reference is made to the accompanying drawings that form a part hereof.The invention may be practiced using these illustrative embodiments.These embodiments are described in sufficient detail to enable thoseskilled in the art to practice the invention. Other embodiments may beutilized, and that logical, structural, mechanical, electrical, andchemical changes may be made without departing from the spirit or scopeof the illustrative embodiments. To avoid detail not necessary to enablethose skilled in the art to practice the invention, the description mayomit certain information known to those skilled in the art. Therefore,the following detailed description should not be taken as limiting. Thescope of the illustrative embodiments is defined by the appended claims.

The term “reduced pressure” as used herein generally refers to apressure less than the ambient pressure at a tissue site that is beingsubjected to treatment. In most cases, this reduced pressure will beless than the atmospheric pressure at which the patient is located.Although the terms “vacuum” and “negative pressure” may be used todescribe the pressure applied to the tissue site, the actual pressureapplied to the tissue site may be significantly less than the pressurenormally associated with a complete vacuum. Consistent with thisnomenclature, an increase in reduced pressure or vacuum pressure refersto a relative reduction of absolute pressure, while a decrease inreduced pressure or vacuum pressure refers to a relative increase ofabsolute pressure.

The term “tissue site” as used herein refers to a wound or defectlocated on or within any tissue, including but not limited to, bonetissue, adipose tissue, muscle tissue, dermal tissue, vascular tissue,connective tissue, cartilage, tendons, or ligaments. The term “tissuesite” may further refer to areas of any tissue that are not necessarilywounded or defective, but are instead areas in which it is desired toadd or promote the growth of additional tissue. For example, reducedpressure tissue treatment may be used in certain tissue areas to growadditional tissue that may be harvested and transplanted to anothertissue location.

Referring to FIG. 1, a reduced pressure treatment system 11 includes aporous pad 20, or other distribution manifold positioned at a tissuesite 15. The porous pad 20 is fluidly connected to a canister 17 by atarget conduit 21. A reduced pressure source 19 is fluidly connected tothe canister 17 by a source conduit 24. In operation, the reducedpressure source 19 delivers a reduced pressure to the tissue sitethrough a fluid communication path, which is collectively comprised ofthe source conduit 24, the canister 17, and the target conduit 21.

A solenoid or other suitable valve 18 is fitted to the source conduit 24and serves to release the reduced pressure within the fluidcommunication path to the atmosphere when opened. The solenoid valve 10may communicate with and be controlled by a processing unit 26, which isdescribed in more detail below. The processing unit 26 may furthercommunicate with a sensing device 28 that is used to determine apressure in source conduit 24.

The reduced pressure treatment system 11 is capable of reliablydetermining the fill status of a canister (i.e. whether the canister isfull or not full of fluid). The system 11 relies on the volume of thefluid communication path being fixed and thus, relief of the vacuum fromthis known volume should occur within a set time after the valve 18 isopened. When the processing unit 26 detects a blockage within the fluidcommunication path by any reliable blockage detection method, theprocessing unit 26 signals the valve 18 to open for a selected amount oftime (e.g. 1 second) to vent the reduced pressure from the fluidcommunication path to atmosphere. The processing unit 26 receivessensing data from the sensing device 28 and monitors the pressure decayover this 1 second period. If the pressure decays quickly, thenprocessing unit 26 determines that the canister 17 is full as the volumeof the chamber being vented is small. Accordingly, the processing unit26 will signal an alarm if a canister full status is determined.

If the decay is slow, which is to say that in the 1 second period thatthe solenoid valve 18 is opened, the vacuum does not decay to apre-determined level, the processing unit 26 will conclude that thecanister 17 is not full. The processing unit will then assume that theblockage condition originally detected is caused by an actual blockagein the target conduit 21 and not a canister full condition. Theprocessing unit 26 in this particular instance may signal a separatealarm to indicate the presence of a blockage. Preferably, the alarmsused to notify a user of a canister full of wound fluid and a blockagein the target conduit 21 through which the wound fluid flows areseparate and distinct.

The decay of the reduced pressure may be determined in several ways. Forexample, the decay may be determined by measuring a reduction in thereduced pressure (i.e. increase in absolute pressure) over a selectedamount of time after opening valve 18. As another example, the decay maybe determined by measuring the amount of time that is required for thereduced pressure to drop to a threshold pressure. The decay in reducedpressure may also be determined by measuring the reduction in the flowrate in the source conduit 24 over the selected amount of time afteropening valve 18. Other methods of measuring the decay of reducedpressure may also be used in a similar manner and are contemplatedwithin the scope of the illustrative embodiments.

Additional components may be employed together with the illustrativeembodiments to better determine the fill status of canister 17. Forexample, the target conduit 21 connecting canister 17 to the porous pad20, through which wound fluids flow, may include optional valve 25.Closing valve 25 at the time of venting to atmosphere through valve 18may indicate the volume within the canister that is empty. Deducing fromthis indication of empty volume and knowing the geometry of thecanister, one may determine the level of fluid in the canister, and alsomay determine fluid flow rate from the tissue site 15 if periodicallymonitored.

Referring still to FIG. 1, but also to FIG. 2, the processing unit 26may be contained within a therapy unit housing 40 that may also housethe reduced pressure source 19, the sensing device 28, and the valve 18.The processing unit 26 may be configured with one or more processorsthat are the same or different types. For example, the processing unit26 may include one or more processors, logic, analog components, or anyother electronics that enable signals including information, such asfluid pressure at various locations in the system to be received.

The processing unit 26 executes software 208 and may further be incommunication with (i) a memory 210 for storing data and software code,(ii) an input/output (I/0) unit 218 for communicating with other devicesand systems, such as a valves or sensing devices, wirelessly, via awire, or via a memory input device, (iii) a storage unit 222 that maystore one or more data repositories 226 a-226 n (collectively 226), suchas a database having one or more files, (iv) an electronic display 234that may or may not be touch-sensitive, and (v) one or more alarms 238that are capable of signaling a user of the reduced pressure treatmentsystem using audio, visual, or other signals. The software 208 may beconfigured to interface with each of the other devices (e.g., electronicdisplay 234) to allow management and observation of the reduced pressuretreatment.

Test Data

With reference to FIG. 3, this figure depicts a graphical representationof the results of a test conducted with a system similar to reducedpressure treatment system 11. In this test, variation in decay time wasnoted against fill level at 125 mmHg for a closed canister. The canisterwas filled with various levels of water from empty to 500 ml in 50 mlincrements. Negative pressure for the wound therapy was set to 125 mmHgand the system run until the pump stopped at slightly over the targetpressure. Therapy was then turned off and natural leakage was applied tobring the pressure down to 125 mmHg. At this point, the valve wasoperated to vent the canister to atmosphere. The pressure profile wasrecorded at 10 samples per second. The same test was also conducted witha standard large wound attached to the system and resulted in the graphsof FIG. 6.

Referring to FIG. 4, this figure depicts a graphical representation ofthe results of a test in which differences in decay times between fulland nearly full canisters at various pressures with large wound wereobserved. A standard large wound foam and dressing was prepared on aplastic base and fitted with a reduced pressure delivery pad to allow asyringe to inject liquid so as to fill the canister and cause a blockagealarm. Two sets of curves were plotted at therapy pressures of 50 to 400mmHg, one at 450 ml fluid level and one with a canister filled by wounddrainage until a blockage alarm occurred. The 450 ml value was chosenbecause as high a fill level as possible was required for the specificcanister used, consistent with no blockage alarm occurring. Thissituation was contemplated to be the worst case scenario with theunderstanding that if the system could differentiate between the twosituations at a high level, it would only be easier as the level isreduced.

The canister was filled to 450 ml and a pressure slightly above thetarget pressure was acquired. The vacuum pump was turned off and asleakage brought the pressure down to the target level, the vent valvewas opened as described above. For the blocked family of curves, thecanister was filled by injecting water into the wound and running undernormal therapy conditions. Results of this test are shown in FIG. 4.

With reference to FIG. 5, this figure depicts a graphical representationof the results of a test in which decay differences between full andother fluid levels at 350 mmHg with a large wound were observed. Astandard large wound was prepared as in the test of FIGS. 3 and 4 andpressure curves plotted at 350 mmHg for fluid levels from empty to 500ml, filling externally. This procedure was done under direct control asin the tests described above. The system was run under normal therapy at200 mmHg and fluid injected into the wound until a blockage alarmoccurred. Direct control was resumed at 350 mmHg and the last curveplotted.

Test Conclusions

The plots obtained with a closed canister in FIG. 3 show good linearitybetween the fill level and the time for the pressure to fall to bothzero and 5 mmHg. There is some crossover in the early stages of thedecay, but the trend of the plots appears to indicate that decay time isapproximately proportional to fill level.

The results depicted in FIG. 3 were for a closed canister. Additionalwork as reflected in FIG. 6 revealed that when a wound is attached, thecross-over effect is considerably reduced.

The graph in FIG. 4 indicates that there is distinct grouping in thedata. With a full canister when filter occlusion had occurred, thepressure fell to under 10 mmHg in less than 0.8 seconds, irrespective ofthe therapy pressure. When the canister is approximately full butocclusion had not occurred, the time to 10 mmHg was three seconds ormore. The differential may have improved if the time to a percentage ofinitial rather than to an absolute pressure were measured.

FIG. 5 confirms that the decay times for all fill levels from empty to500 ml take a substantial time to fall to near-zero levels from 350mmHg. The fastest decay rate (500 ml) fell to about 20 mmHg after fourseconds and was still around 10 mmHg after 10 seconds. By comparison,the blocked curve fell to virtually zero (under 3 mmHg) in less than asecond.

The system and method disclosed in the instant application improves uponexisting negative pressure treatment systems by reliably alerting theuser of the system that the wound fluid canister is full and may have tobe emptied. By releasing the pressure in the fluid communication paththrough a valve, the systems and methods disclosed herein are able tomeasure the decay of the negative pressure. If the negative pressureinside the fluid communication path decays rapidly, then the systemdetermines that the canister is full and activates an alarm notifyingthe user that the canister is full of wound fluid. If the negativepressure inside the fluid communication path decays slowly, then thesystem determines that there is a blockage in the system that should beremoved and notifies the user by activating an alarm.

Even though many of the examples discussed herein are applications ofthe present invention in the medical field of treatment of wounds, thepresent invention also can be applied to other types of negativepressure applications including but not limited to suction and fluidcollection devices for other medical and non-medical uses.

One skilled in the art will see that the present invention can beapplied in many areas where there is a need to provide an indication ofa fill status of a container containing any substance. It should beapparent from the foregoing that an invention having significantadvantages has been provided. While the invention is shown in only a fewof its forms, it is not just limited but is susceptible to variouschanges and modifications without departing from the spirit thereof.

The invention claimed is:
 1. A reduced pressure treatment systemcomprising: a reduced-pressure source; a canister; a source conduitconfigured to fluidly couple the reduced-pressure source to thecanister; a valve in communication with the source conduit; and aprocessing unit in communication with the valve, the processing unitconfigured to open the valve and to determine a fill-status of thecanister based on a decay of reduced pressure in the source conduitafter opening the valve.
 2. The system of claim 1, wherein thefill-status indicates whether the canister is full or is not full. 3.The system of claim 2, wherein the processing unit is further configuredto signal a blockage alarm to indicate a blockage in a target conduit ifthe fill-status is not full.
 4. The system of claim 2, wherein theprocessing unit is further configured to signal a canister-full alarm ifthe fill-status of the canister is full.
 5. The system of claim 1,wherein the processing unit is further configured to signal a blockagealarm if the reduced pressure does not decay to a pre-determined levelwithin a selected amount of time after opening the valve.
 6. The systemof claim 1, wherein the processing unit is further configured to signala canister-full alarm if the reduced pressure decays to a pre-determinedlevel within a selected amount of time after opening the valve.
 7. Thesystem of claim 1, wherein the processing unit is configured to: openthe valve to for a selected amount of time; signal a first alarmindicative of a full canister if the reduced pressure decays to apredetermined level over the selected amount of time; and signal asecond alarm indicative of a blockage if the reduced pressure does notdecay to the predetermined level over the selected amount of time. 8.The system of claim 1, wherein the processing unit is further configuredto: open the valve to for a selected amount of time; determine apressure attained within the source conduit following the selectedamount of time; and determine the fill-status of the canister based onthe pressure attained.
 9. The system of claim 1, further comprising asensing device in communication with the source conduit and configuredto measure the decay of reduced pressure in the source conduit.
 10. Thesystem of claim 9, wherein the sensing device is a pressure sensor. 11.The system of claim 9, wherein the sensing device is a flow sensor. 12.The system of claim 1, wherein the valve is a first valve, and furthercomprising: a target conduit fluidly connected to the canister; and asecond valve fluidly coupled to the target conduit and configured toclose if the first valve is open.
 13. The system of claim 12, whereinthe first valve and the second valve comprise electrically ormechanically-actuated valves.
 14. The system of claim 1, furthercomprising a canister-full alarm in communication with the processingunit and configured to indicate the fill-status.
 15. An apparatus fordetermining a fill-status of a container of fluid in a tissue treatmentsystem, the apparatus comprising: a sensing device configured to sense areduced pressure in a source conduit; a valve configured to release thereduced pressure in the source conduit; and a processing unit incommunication with the sensing device and the valve, the processing unitconfigured to open the valve and to determine a fill level of thecontainer based on a decay of the reduced pressure after opening thevalve.
 16. The apparatus of claim 15, wherein the processing unit isfurther configured to: set a pressure threshold; measure a time for thereduced pressure to attain the pressure threshold; and determine thefill-status of the container based on the time.
 17. The apparatus ofclaim 15, wherein the processing unit is further configured to signal afull-canister alarm if the fill level of the container indicates a fullcontainer.
 18. The apparatus of claim 15, wherein the processing unit isfurther configured to differentiate between a full container and ablocked source conduit based on the decay.
 19. The apparatus of claim18, wherein the processing unit is further configured to signal a firstalarm for the full container and signaling a second alarm for theblocked source conduit.
 20. An apparatus for determining a fill-statusof a container of fluid in a tissue treatment system, the apparatuscomprising: a sensing device configured to sense a reduced pressure in asource conduit; a valve configured to release the reduced pressure inthe source conduit; and a processing unit in communication with thesensing device and the valve, the processing unit configured to: openthe valve and measure a decay of the reduced pressure after opening thevalve, signal a first alarm indicative of a full canister if the reducedpressure decays to a predetermined level over a selected amount of time,and signal a second alarm indicative of a blockage if the reducedpressure does not decay to the predetermined level over the selectedamount of time.